The present invention relates to crankcase ventilation of diesel internal combustion engines, particularly diesel engines used for locomotive applications.
Diesel powered locomotives generally require an absence of positive crankcase pressure. Yet, during the operation of internal combustion engines, blow-by gas from the combustion chamber during the combustion stroke causes a positive pressure in the crankcase which must be relieved. In the case of locomotive applications, it is desired that the crankcase generally be negatively pressured. Accordingly, since a simple valve or opening in the crankcase is inadequate, a crankcase ventilation system is utilized.
The crankcase ventilation system on a locomotive diesel engine evacuates the excessive crankcase air in the crankcase (from seals and piston blow-by) to the exhaust stream and eventually the atmosphere. Included in the crankcase air is an oil mist that has two negative consequences. First, the oil mist contributes to the engine""s emissions; and second, the oil leaves a coke deposit of carbon that can ignite and start railside fires.
FIG. 1 exemplifies a conventional diesel engine crankcase ventilation system 10, including an oil separator 12 and an evacuator 14. A pipe connection 16 communicates generally horizontally with the crankcase, as for example at an upper portion of the oil pan 18. An elbow 20 connects the pipe connection 16 to the oil separator 12, which has an off-set opening 22. Connected to the off-set opening 22 is the evacuator 14. The evacuator 14 has a vertical portion 24 and a horizontal portion 26 demarcated by a bend 28. The end of the horizontal portion 26 is interfaced with an exhaust port 30 which communicates with the engine exhaust system. The bend 28 is fitted with a nozzle assembly 32. The nozzle assembly 32 includes a single orifice nozzle 34 internal to the horizontal portion 26 which is directed down the horizontal portion toward the exhaust port 26, the horizontal portion diameter outwardly tapering with increasing distance from the nozzle assembly. The nozzle assembly 32 is interfaced with a source of pressurized air external to the crankcase, via an air line 36.
In operation, pressurized air emanating from the nozzle blows air toward the exhaust port, causing a low pressure condition in the vertical portion of the evacuator. This low pressure zone communicates with the crankcase through the oil separator to cause crankcase air to be affirmatively evacuated from the crankcase. Oil-laden crankcase air passes through the oil separator, during which the expanded volume and vertical path combine to cause oil to precipitate out of the crankcase air and then flow back into the crankcase.
Several drawbacks of the conventional diesel engine crankcase ventilation system are yet in need of redress, among those being a need to improve the efficiency and effectiveness of crankcase air removal into the exhaust port.
The present invention is a multi-orifice crankcase air evacuator assembly for a diesel engine which provides improved efficiency and effectiveness of crankcase air removal into the exhaust port of the engine.
The multi-orifice crankcase air evacuator assembly includes a multi-orifice nozzle interfaced with an evacuator tube. The multi-orifice crankcase air evacuator assembly is located in a housing which communicates with a crankcase port of the engine so that crankcase air is freely movable into the housing at the multi-orifice crankcase air evacuator assembly. The multi-orifice crankcase air evacuator assembly, in turn, is connected to an exhaust port of the engine which communicates to the engine exhaust system.
The multi-orifice nozzle has a nozzle body connected to an external source of compressed air. The compressed air enters a nozzle chamber of the nozzle body. Connected with the nozzle body is a nozzle head having a number of nozzle orifices, preferably five, each communicating with the nozzle chamber. The nozzle orifices are mutually spaced in a symmetric arrangement (i.e., an xe2x80x9cXxe2x80x9d pattern) so as to collectively provide a generally circumferential area of air movement as the high pressure nozzle air rapidly effuses from the nozzle orifices.
The evacuation tube has a tube body defining a central passage and a bell-mouth concentrically disposed at its inlet, whereat the bell-mouth merges with the central passage to define thereat a throat. The bell-mouth has a generally mushroom shape characterized by an annularly distributed convex air guide surface. The central passage has a near portion adjacent the throat which serves as an air mixer and a distal portion that widens with increasing distance from the bell-mouth and which serves as an air diffuser. At the outlet, the tube body has a flange for interfitting with a connection to exhaust port of the engine.
Operatively, the nozzle orifices are located in alignment with the central passage, in close spaced proximity to the bell-mouth. As high pressure nozzle air exits the nozzle orifices, the respective high velocity nozzle air streams converge at the throat and pass rapidly along the central passage. This nozzle air movement creates a region of low pressure surrounding the bell-mouth. Consequently, crankcase air surrounding the bell-mouth is sucked into the throat at a large rate, and preferably in a generally laminar flow over the bell-mouth. The crankcase air mixes with the nozzle air streams in the near portion of the central passage, causing a momentum mixing therebetween which causes crankcase air to rapidly move with the air streams down the central passage. As this mixed air moves down the central passage, the distal portion of the central passage allows expansion and velocity reduction of the mixed air, whereupon the mixed air has generally achieved atmospheric pressure by the time it reaches the outlet.
The bell-mouth allows for crankcase air to be sucked into the throat over a 360 degree circumference, which contributes to a free and voluminous movement of the crankcase air into the throat. The near portion of the central passage provides an air mixing section where the nozzle air exchanges momentum with the crankcase air. The distal portion of the central passage serves as a diffuser which serves to recover kinetic energy in the mixed air flow stream. The multiple nozzle orifices provide better gas mixing and movement than can be provided by a single nozzle orifice, resulting in better momentum exchange, and reduction of external air capacity to achieve a similar amount of crankcase air pumping.
Accordingly, it is an object of the present invention to provide more efficient evacuation of crankcase air in connection with a crankcase air ventilation system of a diesel engine.
It is an additional object of the present invention to provide improved evacuation of crankcase air in connection with a ventilation system of a diesel engine, wherein a multi-orifice nozzle is coupled with an evacuator tube configured to provide efficient air entry, mixing and diffusion.
These and additional objects, features and advantages of the present invention will become clearer from the following specification of a preferred embodiment.